27/05/2026
After Angelina has needed special care after a mammary lump removal this past week I thought it’s a good opportunity to make a more in depth post.
Tumours are one of the most common ailments pet rats develop with the number one being mammary gland related.
These tumours (fibroadenomas) are benign and encapsulated, appear under the arm pit, chin area or near the groin and are made up of an abnormal replication of cells within the rat’s extensive mammary tissue.
They tend to appear quite fast and are soft and moveable.
A second form of mammary tumour that is rarer can also develop, these tumours are called adenocarcinomas which are firmer and feel attached to muscle, these are not as easily removed as they invade surrounding organs and have the possibility to metastasise by traveling through the lymph nodes and blood vessels to the lungs and bone which can further travel to other areas of the body.
They also tend to show up quite fast but have a similar timeframe of growth before it impacts the rat to the point euthanasia is needed.
Tumours grow at different rates but usually have a timeframe of 3-6 months where removal is fairly straightforward, when they grow too large the risk for removal becomes higher as they will impact close by organs.
Leaving tumours will eventually affect the rats mobility and ability to be able to clean, groom and move around freely, risk of ulceration and necrosis of tissue also becomes high - this is especially dangerous because it can cause blood poisoning and infection (sepsis) which is excruciatingly painful and life threatening.
Leaving the tumour to develop, the rat will eventually experience weight loss, lethargy and a weakened immune system due to the tumour leaching nutrients from other areas of the body so it’s extremely important to have a plan in place and either remove it before it gets to this point or organise euthanasia prior to the rat being affected in this way because their welfare needs to come first and your responsibility as an owner is to ensure you reduce unneeded suffering.
Females have higher incidences than males, this is because during fetal development in males testosterone is released before mammary tissue is fully developed.
These tumours primarily rely on hormones estrogen and prolactin but percentage of occurrence can be reduced by spaying/desexing female rats from 4 months of age although this isn’t needed and comes down to owner preference.
Rats from 12-18 months are most commonly affected with percentages being 30-67% in females and about 18% in males.
Studies vary so below is just one that I’ve found.
https://www.cabidigitallibrary.org/doi/pdf/10.5555/20163321475
https://ratguide.com/health/reproductive/mammary_tumor.php
Diet can also play a part in tumour development so it’s important to make sure you’re feeding a low fat, moderate protein diet with minimal to no processed or high in sugar foods.
Yes, they can still have a sneaky human snack at times but it’s important to supply a species appropriate diet for optimal health which includes fresh veggies, grains, fruits, healthy fats like fish and egg along with their pellets (not the colourful mixed junk from the supermarket!)
https://www.animallama.com/rats/rat-diet-health/
http://www.isamurats.co.uk/feeding-to-support-rats-with-tumours.html
How to best take care of a rat with tumours and reduce risk of them occurring:
🥬Check your rats daily by feeling along the body for any lumps.
🥬Make sure you’re feeding a stable healthy diet.
🥬Make sure your rat is active and stays a healthy
weight.
🥬Check in with your vet for assessment and pain relief.
🥬Change cage set up to make it more accessible if mobility becomes impacted.
🥬Have water and food source on lower levels of the cage for easier accessibility.
🥬Keep an eye on your rats body condition and energy levels.
🥬Watch for discolouration & tightening of skin.
🥬Have a plan ready - either surgery or let the rat live out their days until QOL (quality of life) is impaired to a degree the rat can no longer enjoy life.
Typical surgery for lump removal costs between $400-$700 AU.
Genetics play a part also and ethical breeders aim to reduce health issues overall no matter what they be and although they can’t be irradicated completely they can be reduced over time with good selection and the help of your feedback.
Something to remember though as I know how easy it is to start ticking over in your head and asking yourself, “did I do something wrong” “what else could I have done” “why is this happening, they’re too young” “have I made the right choice?” “Is there something I can do better next time?”.
The answer is almost always - This is part of nature and rats aren’t evolutionarily designed to live long, they are considered geriatric at 18 months and their typical average lifespan is 15-24 months, a good lifespan is 24 months and a great one is upwards of that.
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(Images below pulled from internet)
